Vibrating system



J. P. MAXFIELD.

VIBRATING SYSTEM.

APPLICATION FILED AuG.2a, 1917.

1,434,788, v Patented Nov. 7, 1922.

\\\IIIII Ff? Patented Nov. 7, 1922.

UNITED STATES PATENT OFFICE.

JOSEPH P. MAXFIELD, OF MAPLEWOOD, NEW JERSEY, ASSIGNOR TO WESTERN ELEC-TRIO COMPANY, INCORPORATED, 0F NEW YORK, N. Y., A CORPORATION OF NEWYORK.

VIBRATING SYSTEM.

Application led August 28, 1917. Serial No. 188,582.

7'0 Hui/1.0711 iti/may concern.'

Be it known that I, Josemi P. MAxFI'nLD, a. citizen of the UnitedStates, residing at Maplewood, in the county of Essex and State of NewJersey, have invented certain new and useful .Improvements in VibratingSys tems, of which the following is a full, clear, concise, and exactdescription.

This invention relates to i'liapliragms, and more particularly tophonographic diaphragiiis such as those used in phonographic recordersand reproducers.

The object of this invention is to provide ay diaphragm which will bemore sensitive to a wider range of fiequeiicy than those hei'etofoi'eemployed. A specific object is to' construct a diaphragm having both alow natural frequency and a. higli natural frequency.

Although this invention will'be hereinafter described in connection witha phonographic reproducer or sound box, it is not limited to such anapplication, but may be employed in connection with any suitable `soundrecording, transmitting or receiving device in which a' vibrating membermay he included.

It is well know in the art that a diaphragm clamped at its edges,l as inu sound box for a talking machine or in a telephone transmitter, forexample, does not respond equally for all frequencies of vibrationiinprcssed upon it, but for each diaphragm there is a frequency in theneighborhood of which there will be maximum response, and for otherfrequencies the response will be much less. The frequency for maximumresponse is generally known as the natural frequency of the diaphragm.The value. of this natural frequency for a diaphragm depends upon itselasticity or stiffness and mass, increasing with increase inelasticity, and decreasing with increase in mass. The amount of responsefor any given frequency depends upon the friction, effective mass andthe elasticity of the vibrating system.

For frequencies near the natural period the response is governed mainlyby the friction, being larger the smaller the friction;

above the natural period the effective. mass is the governing quantity,the response being larger the smaller the mass; while below the otherhand, if the diaphragm has a low degree of elasticity and is ofappreciable mass the low notes will be reproduced Well, to the detrimentof the higher toiles.

rl`his invention embodies a diaphragm of such a character that it willreproduce etliciently notes of both low and high frequency. Toaccomplish this, the diaphragm is made non-uniform and capable ofvibrating in two different ways. In the specific embodiment hereinafterdescribed in detail, the diaphragm consists of a centra-l portion of ahighly elastic material 'having a high natural fre( uency and an outerortion composed of a flexible membrane. en such a diaphragm is clampedbetween suitable clamping arms and a stylus bar carrying the reproducingor recording needle is fastened to thecentral portion of the diaphragmand vibrations of low frequency are impressed on the diaphragm, theentire diaphragm will undergo displacements on account of the lownatural frequency of the outer ortion. Of course, the natural frequencyof vibration of the outer portion of the diaphragm is lowered somewhatby the addition of the mass of the central portion, and is also modifiedto sonic extent by the fact that the central portionis connected to thest lus bar. The central portion on account o its high natural frequencywill not vibrate of itself, but will act asa plunger. When, however, theoscillations impressed on the diaphragm are of high frequency, thecentral portion, on account of its hioh natural fre ueiicy, vibratesreadily, whi e there is fectively responds to both low and highfrequencies, as well as those intermediate in value.

For the better understanding ofy this invention, reference is made tothe accompanying drawings, in which Fig. 1 represents a cross-sectionalview of this invention as embodied in a phonographic sound box; Fig; 2illustrates the top view of a portionY of the same; and Fig. 3 is across-sectional view of a diaphragm.

ln the embodimentof this invention illustrated in Fig. '1, 4 is asounding box suitably fastened to the frame or diaphragm holder 5. Aflange 6 of the frame serves to clamp the diaphragm 7 between two rubbergaskets 8 and 9. Upon the frame 5 is mounted a bracket 12, which, bymeans of the knife edges 13 (see Fig. 2), supports a socket 14 adaptedto receive a stylus needle. The stylus bar 17 is fastened at one end tothe socket 14 and at the other end is fastened to the central portion dfthe diaphragm 7. Suitable tension on the stylus and diaphragm isobtained by the springs 18 (see Fig. 2). Diaphragm 7 has an outerportion 19 of flexible material and a central portion `20 of a highlyelastic material. rlhe stylus bar 17 is shown attached to said centralportion: lf we assume that the stylus needle is impressing vibrations oflow frequency upon the diaphragm, the whole diaphragm will undergodisplacements on account of the low natural frequency of the flexiblematerial which composes the outer part of the diaphragm. The stiffcentral portion 20 will not vibrate of itself but will act merely as aplunger attached to the stylus bar 17. When, however, the impressedvibrations are high, the stiff central portion will of itself undergovibrations on account of its high natural period, while thedisplacements of the remainder of the diaphra-gm`will be negligible. Ithas also been found, providing the stylus bar and the diaphragm are ofminimum mass, that for vibrations of intermediate frequency 'between thetwo natural frequencies the diaphragm responds elliciently, although theresponse is not as great as for frequencies near one of the natural freuencies.

ig. 2 shows more in detail the of the stylus bar to its supportingstructure.

. The stylus bar 17 is shown to'have two arms 25 and 26, which arepivoted on two knife edges 13, 13. The two tensioning springs 18, 18extend from the bracket 12 to the arms 25, 26. Since the stylus bar andits supporting arms are also part of the moving system, it is preferablethat the eective mass of the stylus should be as small as possible, forotherwise, as stated previously, the response for frequencies on eitherside of the natural frequency would be inefficient. Itis, therefore,preferable that the stylus rel ation mames bar should be made of somelight material such as aluminum.

All of the above structure, except that of the diaphragm and the lightmass stylus bar, is well-known in the art and is described merely toenable the application of this invention to be more. readily presented.

Fig. 3 is a cross-sectional view of the diaphragm showing in detail itsstructure. 3() and 31 are two thin sheets of a flexible material, suchas paper, cemented together near their outer edges. Between the twosheets, and suitably cemented together and to the paper sheets, arethree discs 32, 33 and 34, of some suitable highly elastic material suchas wood or steel, for example. lt is preferable that the dia-meter ofthese discs should be from one-third to five-sixths of the diameter ofthe sheets of paper, although the ratio may have any suitable value,depending upon the material composing the discs and the other vibratingparts. The discs shown are made of wood and have their grains crossed insuch a manner that warping is prevented. Any number of discs may be usedin order to obtain the desired stiffness; in the case of metallic discsonly one would be necessary. It has been found convenient to use twosheets of paper and to cement the discs in between the sheets, but suchan arrangement is not essential, as the discs may be cemented on theoutside, in which case only one sheet of paper could be used. Themembranes between which the discs are suspended may be of any suitableflexible material such as paper, oiled silk, or parchment. It is readilyseen that such a diaphragm is not limited to lthe supporting structureillustrated in Fig. 1, as it may be used in connection with any soundbox desired, or in connection with any suitable structure in which avibrating.- member is employed.

What is claimed is:

1. A diaphragm. comprising a plurality of wooden discs of approximatelythe same diameter and cemented together, a thin sheet of paper cementedto each side of said discs, said sheets extending beyond the edges ofsaid discs and having their extending portions cemented together, thepart of said diaphragm within the perimeter of said discs having anatural frequency of vibration corresponding to a high musical note.

2. A diaphragm comprising two flexible membranes cemented together, adisc of small mass suspended between said membranes, a part of saidmembranes extending beyond the perimeter of said disc and having anatural period corresponding to a low musical note and the portion ofsaid diaphragm lying within the perimeter of said d isc having a naturalfrequency of vibration corresponding to a high musical note,

whereby said portion is adapted to vibrate within itself enbeenntieuyindependent ef the remainder of Said diaphragm for vibrations of thenatural frequency of said portion.

3. A diaphragm comprising two thin `sheets of paper cemented together,and a plurality of wooden discs between said sheets at theircentralfportion adapted to act as a plunger when the whole diaphragm isvibrating, the part of said diaphragm within the perimeter of said discshaving a natural frequency of vibration corresponding toa high musicalnote,

4. A diaphragm having a natural period corresponding to a. low musicalnote and comprising a central portion of small mass and a flexibleportion, said central portion having a natural period corresponding to ahigher musical note and comprising a disc of stili', highly elasticmaterial, and saidk flexible portion being of larger diameter than saiddisc and forming a flexible mounting for said disc, 3

5. A vibratory system comprising a stylus bar and a diaphragm, thestylus bar and the diaphragm as a whole having a natural periodcorresponding to a low musical frequency, said diaphragmcomprisingacentral portion of small mass and a exible portion, saidcentral portion having a'natural period corresponding to a highermusical frequency and com risin a disc of stiff, highly elasticmaterlal, said flexible portion being of larger diameter than said discand forming a flexible mounting for said disc, the effective mass of thestylus bar and of the diaphragm each being small, whereby the system ishighly responsive to musical frequencies other than saidtwo musicalfrequencies.

. 6. A vibratory system comprising a dia-- phragm and having a naturalperiod corresponding to a low musical fre uency, said diaphragmcomprising a centra portion of small mass and a exible portion, saidcentral portion having a natural4 period corresponding to a highermusical frequency and comprising a dlsc of stiff, highly elastic-material, said flexible portion being of J OSEPH P. MAXFIELD.

